The image forming system of liquid crystal display devices has polarizing films placed as essential components on both sides of glass substrates that form the liquid crystal panel surfaces. A polarizing film generally used includes a polarizer and a protective film or films bonded to one or both surfaces of the polarizer with a polyvinyl alcohol-based adhesive or any other adhesive, in which the polarizer includes a polyvinyl alcohol-based film and a dichroic material such as iodine.
Polarizing films also have a problem in that in a harsh environment accompanied by thermal shock (e.g., a high-temperature test at 95° C. for 250 hours), the polarizer undergoes changes in shrinkage stress, so that cracks can easily occur entirely in the direction of the absorption axis of the polarizer. In other words, polarizing films have insufficient resistance to thermal shock-induced cracking in the harsh environment. In particular, a one-side-protected polarizing film including a polarizer and a protective film that is provided on only one surface of the polarizer for thickness reduction has a problem in that excessive stress can occur inside the polarizer due to the difference between the shrinkage stress on the protective film side of the polarizer and the shrinkage stress on the opposite side of the polarizer from the protective film, so that various cracks can easily occur, including very small cracks of several hundred μm in the absorption axis direction of the polarizer and through cracks passing through the entire surface.
In order to suppress the occurrence of the cracks, for example, it is proposed to provide a pressure-sensitive-adhesive-layer-attached polarizing film including a one-side-protected polarizing film, a protective layer provided on the polarizing film and having a tensile elastic modulus of 100 MPa or more, and a pressure-sensitive adhesive layer provided on the protective layer (Patent Document 1). It is also proposed to provide a pressure-sensitive-adhesive-layer-attached polarizing film including a polarizer with a thickness of 25 μm or less, a protective layer provided on one surface of the polarizer and including a product obtained by curing a curable resin composition, a protective film provided on the other surface of the polarizer, and a pressure-sensitive adhesive layer provided on the outer side of the protective layer (Patent Document 2). The pressure-sensitive-adhesive-layer-attached polarizing films described in Patent Documents 1 and 2 are effective in terms of suppressing the occurrence of cracks. In view of suppression of the occurrence of cracks, thickness reduction, and weight reduction, it is proposed to form a protective layer on at least one surface of a polarizer from a water-soluble, film-forming composition (polyvinyl alcohol-based resin composition) (Patent Document 3).